Hypoxia-induced behaviors of the ctenophore Mnemiopsis leidyi

Abstract

The hypoxia-associated behaviors of the ctenophore Mnemiopsis leidyi are not well understood, despite the ecological significant of this species and the widespread nature of hypoxic (low oxygen) events. The interface of hypoxic and normoxic water (the oxycline) is also associated with suspended sulfur-reducing bacteria, which provide a source of food to plankton and other animals. Wild-caught specimens of M. leidyi were exposed to an artificially-created oxycline (PO2 >140 Torr above, <60 Torr below) in the laboratory and the time the animals spent physically touching this oxycline was quantified. We found that these animals spent a disproportionate amount of time in the oxycline location, suggesting that they are able to sense the oxycline based only upon the oxygen gradient. M. leidyi specimens were also exposed to an artificial, discrete oxygen source in order to mimic the availability of oxygen from aquatic photosynthetic plants and algae. Animals associated with this oxygen source apparatus by wrapping their oral lobes around it or lingering within 2 cm. Specimens in hypoxic (<60 Torr PO2) conditions were 18.7 times as likely to associate with this apparatus as animals in aerated water (>140 Torr PO2) (p=0.0088), suggesting that M. leidyi may be able to utilize aquatic photosynthetic plants and algae as an oxygen source during hypoxic events. Given the increases in marine hypoxia worldwide, these behaviors by a well known invasive species may represent a previously unexplored ecological impact.